Dehumidifying element and manufacturing method for the same

ABSTRACT

A dehumidifying element includes a super absorbing polymer (SAP), and a hygroscopic base, thereby maintaining hygroscopic characteristics regardless of aging and a high humidity absorbing rate and needing a smaller amount of energy for regeneration.

The present application is a divisional reissue application of U.S.patent application Ser. No. 12/698,842, filed Feb. 2, 2010, now U.S.Pat. No. Re. 42,282 which is a reissue application under 35 U.S.C. §251of U.S. patent application Ser. No. 10/500,254, filed Nov. 29, 2004, nowU.S. Pat. No. 7,326,363, issued Feb. 5, 2008, which claims priority toInternational Application No. PCT/KR02/02456, filed Dec. 27, 2002, whichclaims priority to German Application No. 101 64 632.1-43, filed Dec.27, 2001, the disclosure of each which is hereby incorporated byreference in its entirety for all purposes.

TECHNICAL FIELD

The present invention relates to a desiccant, dehumidifying element anda manufacturing method for the same.

BACKGROUND ART

A humidity exchanger element dehumidifies gas by sorption mechanism ofthe desiccants such as aluminum oxide-silicate or titaniumsilicate/titanium-aluminum silicate.

According to U.S. Pat. No. 5,505,769, the elements can be included in asheet composed of inorganic fiber, or can be included in a device formedby the sheet.

However, the conventional humidity exchanger element necessitatesregeneration at excessively elevated temperatures (approximately 90˜150°C.). In addition, the element has demerits that a sorption capacitythereof is limited and that it causes a large amount of pressure loss ofsupply air for being dehumidified. Also, a sorption capacity of thehumidity exchanger element is decreased over time, that is, the elementis greatly influenced by aging.

Also, nucleus and bio-film are formed while the element dehumidifies,thereby closing pores of the humidity exchanger element.

According to G. Heinrich's paper entitled “sorption-supportedair-conditioning” published by the C.F. Müller Publishing Company in1997, the dehumidifying element is made by containing lithium chloridein corrugated cardboard, wherein hygroscopic characteristics of thelithium chloride are used for dehumidifying.

However, The humidity exchanger element containing lithium chloride cannot be used in highly humid environment. This is because the lithiumchloride tends to liquefy after absorbing the moisture in the airespecially in a highly humid condition.

That is, when a solid lithium chloride is changed into a liquid lithiumchloride and the cellulose, the carrier thereof, comes to be unable toabsorb and maintain the liquid lithium chloride due to its limitedsorption capacity, then excessive liquid lithium chloride is drippingaway from the element resulting in a reduced content of the lithiumchloride in the element.

DISCLOSURE OF THE INVENTION

Therefore, an object of the present invention is to provide a desiccantand a dehumidifying element which shows high humidity absorbing capacitywithout the aging influence while necessitating a small amount of energyfor regeneration and a methods for fabricating the same. To achievethese and other objects and advantages and in accordance with thepurpose of the present invention, as embodied and broadly describedherein, there is provided a desiccant which has an improved sorptioncapacity prepared by the ionic modification of a super absorbing polymer(SAP) through contacting it with a salt solution.

There is also provided two methods for fabricating a dehumidifyingelement. The one method for fabricating a dehumidifying element whichconsists of a desiccant itself, comprises a step of selecting a saltsolution; a step of drying a super absorbing polymer (SAP), a step ofcontacting the dried SAP with the salt solution; and a step of drying ahydrogel generated by the contact between the SAP and the salt solution.

There is provided another method for fabricating a dehumidifying elementwhich comprises a step of engaging a SAP to a carrier; a step of dryingthe carrier to which the SAP is engaged; a step of selecting a saltsolution; a step of contacting the carrier with the salt solution inorder to perform an ionic modification of the SAP; and a step of dryingthe carrier to which the SAP is engaged.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view showing a porous carrierincluding fibers and granules having a super absorbing polymer (SAP), inwhich the granules are applied to an upper portion thereof;

FIG. 2 is a longitudinal sectional view of a porous carrier having awave shape of a trapezium and formed by a structured sheet;

FIG. 3 is a perspective view of the porous carrier of FIG. 2; and

FIGS. 4A, 4B, and 4C are schematic views showing methods by which threedimensional channels are generated in which the plural porous carriersare structured and/or flat sheets are arranged.

MODE FOR CARRYING OUT THE PREFERRED EMBODIMENTS

The present invention will now be described with reference toaccompanying drawings.

The desiccant according to the present invention is prepared by theionic modification of a super absorbing polymer (SAP). The desiccant canabsorb more than four times larger amount of the moisture as comparedwith conventional desiccants such as silica-gels and zeolites. When therelative humidity is 50%, the desiccant can absorb the moistureapproximately as much as its dry mass.

A hygroscopic salt such as lithium chloride is used in the ionicmodification of the SAP. It has been found that the hygroscopic saltsuch as lithium chloride has an excellent bonding force with the SAP bysubstitution of Na⁺ by Li⁺).

That is, by the bonding with the SAP, the hygroscopic salt is preventedfrom weeping after absorbing moisture from the air. At the same time,the hygroscopic characteristics of the SAP are improved enormously bythe ionic modification with the hygroscopic salt.

One of the most important finding as in the present invention is thatthe improvement in the sorption capacity by the ionic modification isstrongly dependent upon the concentration of the hygroscopic saltsolution. When too high concentration of the salt solution is used inorder to allow the SAP to contact with sufficiently large amount ofhygroscopic salt ions, the salt solution is found not to be absorbed atall or completely into the SAP. The reason for this is considered thatthe swelling of the SAP is restrained in a high concentration of thesalt solution and thus the amount of the absorbed solution into the SAPis reduced. Consequently, the ionic modification is not performed to aproper extent and the sorption capacity is not improved sufficiently.

On the other hand, if too low concentration of the salt solution isused, the absorbed amount of the salt ions is not sufficiently largeeven though the SAP absorbs large amount of the liquid solution. As aconsequence, the ionic modification thereof is not performed to a properextent and the sorption capacity is not improved sufficiently.

The hydrogel generated by contacting the SAP with a salt solution can bechanged into a proper state capable of absorbing moisture via a step ofdrying.

In the present invention, the preferable SAPs include polymers andcopolymers in which acryl acid and acrylamide are weakly cross-linked,and propfpolymers graft polymers of starch, cross-linked amylum, andcellulose derivative.

The dehumidifying element including the SAP can be fabricated to have apredetermined shape, can be contained in a container formed of materialwhich permits gas to pass, or can be contained in a porous carrier orattached to an outer surface of the porous carrier. That is, thedehumidifying element can be constructed variously.

The dehumidifying element including the SAP can be formed with granules,and the dehumidifying element formed with the granules is contained in acontainer through which air passes or fixed on a carrier having apredetermined shape.

In case that the dehumidifying element is formed with granules, aparticle diameter of the respective granules is selected in a range of0.1 μm˜10,000 μm; grain fraction in a range of 1 μm˜5,000 μm is morepreferable, and grain fraction in a range of 20 μm˜1,000 μm is mostpreferable.

The base of the SAP is a water swelling polymer and/or copolymer basedon (methyl-)acryl acid, (methyl-)acrylonitrile, (methyl-)acrylamide,vinyl-acetate, vinyl-pyrrolidone, vinyl-pyridine, maleic acid(anhydride), itaconic acid (anhydride), fumaric acid, and vinyl sulfoneacid, base, amide, N-alkyl derivative, N,N-dialkyl derivative andfive-acid ester which can be polymerized, or natural ingredients such asa product made of rubber, that is, carboxymethyl cellulose, xanthanalginate, gum Arabic, hydroxyethylcellulose, methylcellulose, starch andamylum derivative, and a product of said components combined orpartially cross-linked.

When the dehumidifying element including the SAP is realized as fibers,it can be used in many fields. Especially, if the porous carrierincludes the dehumidifying element including the SAP, the dehumidifyingelement can be realized as a textile, meshed textile, knitted fabric,knit, or bonded fabric. It is also possible to combine theaforementioned embodiments of the porous carrier.

Methods for providing the dehumidifying element including the SAP in thecarrier or on a surface of the carrier include a method for coating thedehumidifying element on the porous carrier or a method for insertingthe dehumidifying element in the porous carrier.

Preferably, by realizing the porous carrier as a fiber composite formedof natural fiber and artificial fiber, humidity carrying characteristicsof the natural fiber and mechanical characteristics of the porouscarrier formed by the artificial fiber can be improved.

The porous carrier can be formed with a single layer or multiple layers,or can be flat or structured. Herein, if the porous carrier is formedwith one or plural sheets, it is formed as a dehumidifying body alongthe periphery of which air flows along, or which air passes through.More preferably, the sheet is structured by forming a wave-shape of thesheet as a trapezoid or a triangle in a horizontal sectional surface.Then, plural and smooth sheets are arranged in such a method thatspatial 3-dimensional channels are generated. Through the channels, airfrom which humidity will be removed is guided.

Then, the hygroscopic characteristics of the element fabricated in the3-dimension shape can be realized by selecting the salt solution.Regardless of the realization form that the SAP takes a granular form orthe SAP is included in the carrier, by drying the SAP at first, the SAPcan absorb the salt solution much more. According to this, the SAP canbe contacted to the hygroscopic salt. The SAP is provided with thehygroscopic salt by contacting the salt solution with the SAP. Thehydrogel generated by contacting the granules with the salt solution orSAP is dried, thereby being converted into a state capable of absorbingmoisture.

When the granules of the SAP is engaged to each other and forms largeagglomeration, it is preferable that the agglomeration of the SAP iscrushed to pieces and the granules are classified before contacting withthe salt solution. According to this, uniform characteristics of theelement can be realized. Likewise, if the SAP is engaged to each otherand forms large agglomeration after the step of final drying, it is alsodesirable that the agglomeration of the modified SAP is crushed topieces and the granules are classified.

Another method for fabricating a dehumidifying element with an SAPdesiccant modified ionically is making contact the carrier including theSAP with a salt solution.

If the carrier including the SAP is contacted to the salt solution,dried slowly, and the drying temperature is increased slowly, anadequate regeneration is possible and the salt solution is excellentlyabsorbed by the SAP. On the contrary, it has been observed that the saltis extracted from the surface of the carrier instead of being absorbedperfectly into the SAP when the regeneration temperature is increasedfast to level.

The most important in the preparation of the desiccant is to select theconcentration of the salt solution between 5-15 wt %. In case of usingthe salt solution of the concentration between 5-15 wt %, the sorptioncapacity of the modified SAP can be optimized between the restrictionsin the liquid sorption capacity and in the highest concentration of thesalt solution. That is, the hygroscopic salt of the maximum amount canbe contacted to the SAP by selecting the salt concentration between 5-15wt %, or more preferably as 10 wt %. The reason is that the saltsolution cannot be absorbed properly into the SAP in case of using toohigh concentrated solution due to the inherent characteristics of theSAP restraining itself from swelling in high ion density, and that thesalt ions are not absorbed sufficiently into the SAP in case of usingtoo low concentrated solution due to the limitation on the liquidsorption capacity of the SAP.

When the carrier including the SAP of a granular form is contacted withthe salt solution, if the absorption capacity for the salt solution ofthe SAP is very high, the granule particles tend to be agglomerated toform a large lump after a step of drying. Therefore, it is preferredthat the carrier is contacted with the salt solution in several steps.At this time, at each step, the carrier is partly contacted with thesalt solution, and the contact is realized by drizzling, sprinkling,spraying, etc.

Preferred Embodiment

FIG. 1 is a longitudinal sectional view of the dehumidifying elementaccording to the present invention.

As shown in FIG. 1, the dehumidifying element of the present inventionis composed of a porous carrier 2 to the surface or the inside of whichSAP is attached. The SAP is formed in the porous carrier or at a surfacethereof as granular particles 1.

The granular particles 1 include the SAP, and the SAP is contacted to ahygroscopic base (not shown). At this time, the carrier 2 consists offiber composed of natural or composite polymer and a filament. Further,the carrier 2 includes fibers 3 containing the SAP therein, in which thefibers 3 are inserted into the porous carrier 2. The fibers 3 arecontacted to the hygroscopic base in a finely distributed form like thegranules 1, and can be applied to a surface of the porous carrier 2.

A particle diameter of the granules 1 is approximately identical for allgranular particles and is in a range of 20 μm˜1,000 ˜m. Less preferably,but always suitably, a diameter of grain fraction is in a range of 1˜m˜5,000 μm, in which particles of 20 μm˜1,000 μm are basicallyconsidered. The SAP forming the granules includes polymer and copolymerin which acryl acid and acrylamide are weakly cross-linked, and amylumand cellulose derivatives corresponding to propfpolymer graft polymer ofstarch and cross-linked.

Also, the granules 1 having a hygroscopic base as a finely distributedshape can form the carrier itself without an additional carrier andperform a dehumidifying function. Also, the granules 1 can be applied onthe surface of the porous carrier 2 by coating and included in theporous carrier 2. Also, in case that the porous carrier 2 is a fibercomposite, the SAP can be integrated in the carrier 2 as a part of thefibers.

The fiber composite is a matrix and includes natural fibers or one orplural artificial fiber materials corresponding to reinforcing fibers.The artificial fiber material improves mechanical characteristics of theporous carrier 2 or the fiber composite, and the natural fiber carrieshumidity better.

Also, the natural fiber stores its humidity, that is, water vapor, wateror aqueous solution. The porous carrier composed of fiber or filamentincludes textile, meshed textile, knitted fabric, knit, a combinationtherebetween, bonded fabric, etc.

The SAP is contacted to the hygroscopic base by soaking a water-basedsolution of the hygroscopic base into the granules of the SAP or the SAPfibers, drizzling, sprinkling or by other methods. Herein, the SAPabsorbs the salt solution by its own absorption characteristics.

As a modification method, the modification of the SAP, in other words,contacting the SAP with the salt solution, the SAP can be modifiedbefore the granules of the SAP or the SAP fibers are included in thecarrier or at a surface of the carrier, or can be modified after the SAPgranules or the SAP fibers are already included in the carrier or at thesurface of the carrier.

If the porous carrier is modified in several fabrication steps,structured, or arranged, the modification of the SAP and the saltsolution can be performed at any fabrication step in consideration witha time point of the most preferable modification.

In order to modify the SAP granules or the SAP fibers, first of all, thesalt solution has to be selected. The salt solution includes a stronghygroscopic base such as lithium chloride, magnesium chloride, calciumchloride, or lithium bromide, and includes water as solvent.

The salt solution is completely desalinated, deionized, and distilled,wherein a base concentration is 5˜15 wt % and a maximum concentration is15 wt %.

In order to maintain the residual content of the moisture in the SAP toa minimum extent and thus to allow the SAP to absorb the salt solutionas much as possible in contacting with the salt solution afterwards, itis necessary that the granules or fibers be dried completely beforecontacting with the salt solution. For this purpose, a vacuum drier canbe used preferably. The vacuum drier exerts very small thermal influenceon the granules at the time of drying, thereby preventing a stabilitydepreciation by temperature change through a long term view.

Then, the dried SAP granules are modified ionically by the saltsolution, and can be variously processed. For example, the SAP granulescan be provided in the salt solution or the solution can be added to thegranules.

After the ionic modification, the hydrogel generated from the SAPgranules is dried, thereby regenerating the granules. The hydrogel canbe layered on a plate as thin as possible thereby restricting theformation of the lump in the step of drying. In case of lump formation,it is necessary to crush the lump. It is suitable to use an impactcrusher or a breaker for this end.

When the SAP granules or the SAP fibers are located within the carrieror thereon, in order to perform an ionic modification of the SAP,firstly it is required for the carrier including the SAP to be dried,thereby reducing the amount of the water contained therein to a minimumextent. And the selection of the salt solution is carried out similar tothe aforementioned methods.

When the porous carrier 2 including the SAPs 1 and 3 is contacted withthe salt solution, it would be better to contact in multistage pluraltimes between the porous carrier 2 and the salt solution. The reason isthat the granular particles 1 can be engaged and agglomerated into alump in or on the porous carrier 2. Although it is possible to crush alump formed through an ionic modification of the SAP itself, it would beimpossible to crush a lump formed through an ionic modification of a SAPengaged into a carrier. Therefore, it is important to restrict thegeneration of the lump in a step of contacting the carrier containingthe SAP with the salt solution. The solution can be prudently contactedwith the carrier including the SAP in multistage by drizzling,sprinkling, or spraying.

Finally, the carrier 2 including the SAP is dried slowly, wherein thedrying temperature is gradually increased through the drying processuntil it rises to the maximum regeneration temperature.

This step of slowly drying of the carrier 2 including the SAP by slowlyincreasing the temperature causes to maintains the structure of themodified SAP. That is, the SAP is not decomposed. The drying methodincludes a freeze drying, a microwave drying, a normal drying, or acombination drying therebetween.

A method for fabricating the dehumidifying element, which is formed toincrease the contact area with air, with modified SAP granules or themodified SAP fiber can be properly performed. The structure of theporous carrier, as shown in FIGS. 2 and 3, includes a trapezoid waveshape as a structured sheet, and at the same time, a sheet of acorrugated reed shape has a ripple of 2.5˜7 mm, an interval length (a),a ripple of 1˜5 mm, and a wave height (b).

The forming is attained by an embossing process using a rippling or astamping in heat reaction at a 180° C. temperature.

FIGS. 4A, 4B, and 4C are schematic views showing the respectiveembodiments in which the plural sheets according to FIGS. 1 and 2 arearranged by a method such that 3-dimensional channels are generated.

The channels permit gas from which the humidity will be removed, forexample, air, to penetrate or to flow at the periphery.

In FIG. 4A, one structure is generated by a combination between flatsheets and shaped sheets. The structure is coiled to the dehumidifyingbody simply or laminated, thereby properly being arranged like a generalhumidity exchanging body.

FIG. 4B shows two sheets structured as a trapezoid. The sheets form ahoneycombed structure, and form 3-dimensional channels like in FIG. 4A.Through the channels, gas from which humidity will be removed can flow.

FIG. 4C illustrates a plurality of layers according to the arrangementof FIG. 4B, by which a dehumidifying body having 3-dimensional channelscan be formed.

Regardless of the point in time of the ionic modification, that is,regardless of whether the SPA granules or the SAP fiber is contacted tothe hygroscopic base or not, whether the SPA granules or the SAP fiberis contacted to the hygroscopic base with a location in the porouscarrier or thereon or not (FIG. 1), or whether the modification isstarted after the porous carrier passes several transformation steps ornot (FIGS. 3, 4B, and 4C), lithium chloride adjacent on the surface ofthe SAP permits not only water to be added but also water to be guidedinside of the superabsorber.

At this time, preferably, on one hand, the base is spontaneouslyregenerated as water is guided into the superabsorber. And, on the otherhand, humidity is removed into the superabsorber and thus does notremain on the surface any longer.

INDUSTRIAL APPLICABILITY

As so far described, according to the dehumidifying element and themethod for fabricating the same, hygroscopic characteristics regardlessof aging and high humidity absorbing rate are maintained and a smallamount of energy for regeneration is required.

1. A method of preparing a desiccant comprising the steps of: selectinga salt solution; drying a super absorbing polymer (SAP); contacting thedried SAP with the salt solution in order to perform an ionicmodification of the SAP; and drying a hydrogel generated by the contactbetween the SAP and the salt solution.
 2. The method of claim 1, whereinthe concentration of the salt solution is between 5-15 wt %.
 3. Themethod of claim 1, wherein the salt solution comprises water as asolvent.
 4. A method of making a dehumidifying element comprising thesteps of: engaging a SAP to a carrier; drying the carrier to which theSAP is engaged; selecting a salt solution; contacting the carrier withthe salt solution in order to perform an ionic modification of the SAP;and drying the carrier to which the SAP is engaged.
 5. The method ofclaim 4, wherein the concentration of the salt solution is between 5-15wt %.
 6. The method of claim 4, wherein the salt solution compriseswater as a solvent.
 7. The method of claim 4, wherein the carrier iscontacted with the salt solution by soaking or spraying the saltsolution into the carrier.
 8. The method of claim 4, wherein the step ofcontacting the carrier with the salt solution is repeated.
 9. Adehumidifying element, comprising: a superabsorbing polymer (SAP); ahygroscopic salt contacted with the SAP; and a porous carrier configuredto contain the SAP and the hygroscopic salt.
 10. The dehumidifyingelement of claim 9, wherein the SAP is formed with granules having adiameter equal to or less than 1,000 μm.
 11. The dehumidifying elementof claim 9, wherein the hygroscopic salt includes one of lithiumchloride, magnesium chloride, calcium chloride, and lithium bromide. 12.The dehumidifying element of claim 9, wherein the porous carrierincludes a 3-dimensional channel through which air having humidity to beremoved is guided.
 13. The dehumidifying element of claim 12, whereinthe carrier is a fiber composite of natural fiber and artificial fiber.14. The dehumidifying element of claim 12, wherein the SAP is containedin the carrier while being contained in a textile, meshed textile,knitted fabric, knit, or bonded fabric.
 15. The dehumidifying element ofclaim 9, wherein the SAP comprises an acryl acid cross-linked with atleast one of acrylamide, starch, and cellulose.
 16. The dehumidifyingelement of claim 9, wherein the SAP includes polymer in which acryl acidand acyrlamide are cross-linked.
 17. The dehumidifying element of claim9, wherein the SAP includes polymer in which amylum and cellulose arecross-linked.